The present invention relates to an arrangement for measuring the material moisture or a medium which forms the dielectric or a measuring conductor by determining its dielectric coefficient wherein, by means of a signal generator, a pulse signal is introduced into the measuring conductor at one end and, a receiver arranged at the same end receives the signal reflected from the other end or the measuring conductor and, in a time measuring device, the time elapsed between the start or signal introduction and reception or the reflected signal is determined.
Various methods and apparatus for determining the material moisture or a medium are known including chemical methods and electrical methods: For example, material moisture can be measured by way or measuring the electrical conductivity or the medium. Often this method is preferred because it requires only simple apparatus and can therefore be performed relatively inexpensively. It also permits continuous and practically delay-free measuring or the material moisture.
It is also possible to measure material moisture by determining the dielectric coefficient or the medium since there is a monotonic clear interrelation between the dielectric coefficient or a medium and its moisture content. The dielectric coefficient can be determined, for example, by means of an arrangement in which the medium to be measured is disposed between two plates and the inductive capacity of this arrangement is then determined. Such an arrangement, however, causes problems as to measuring procedures and the size of the capacitor plates is generally objectionable.
With the so-called echo method as disclosed in Applicant's U.S. Pat. No. 5,212,453 the above-referred to problems do not occur. The conductor takes the form of an open duct of finite length and known geometry. It has an electrical connection via which an electric pulse is introduced into the conductor and the time delay of the return of the echo from the end of the conductor is measured. It is known to provide the conductors in the form of two parallel needles which can be inserted into the medium to be measured. From the delay time of the echo the dielectric coefficient of the medium, and therefrom its moisture content, can be determined.
The needles however have to be relatively long in order to achieve high sensitivity, and because of the great length of the needles their utilization and handling is often somewhat complicated.
It is the principal object of the invention to provide an arrangement for measuring material moisture of this type which provides for high sensitivity and is also easy to handle.